A town giving financial assistance to a company to help build an amusement park isn't a bad idea. It generates all kinds of things...tourist dollars, jobs, tax revenue, exposure, so it's worth the money. The problem arrives when tourism becomes a crutch on which any certain city stands upon (cough Orlando cough). It's not a very steady one. Still, as long as the company is competent, it's a good idea to help.
From Legoland's perspective, Kansas City is nowhere near Souther California in terms of population and I have to wonder if the new park can draw anywhere near the same attendance in such a small market. This is especially true because there is so little else going on in KC that would help the park draw tourists to the area. It seems to me that if they could have located near another family oriented park like Dollywood, it would have been a much stronger choice. Those two parks seem like they would draw similar crowds and could really help feed each other.
Hopefully all involved have done their homework and already thought through all of these issues and the park will be a success. I certainly with them luck with it.
If Legoland wants to be in the U.S. Midwest, I'd think that Chicago would make a far more lucrtive choice, with a much larger local population and a major airport.
If Legoland wants slightly better weather and less competition, Indianapolis has been trying to land a theme park for the White River State Park downtown for nearly 20 years. With plenty of hotels and a couple other family friedly attractions in the same area (the zoo and the NCAA hall of fame), Legoland would fit in well in downtown Indy.
In either case, the new Legoland would be located within a 2-4 hour drive of many other major metro areas. In Kansas City, there's St. Louis down the road and... well, nothing. It's the western outpost of the Midwest.
Looking within the park, Legoland's attractions are built for individual kids' play, not for putting through 2,000 guests per hour. So perhaps Legoland wants their parks to be a little incovenient to visit. That helps keep the guest count reasonable while ensuring that the families who come really want to be there, as opposed to people who dropped in only because they were in the area and it seemed like the tourist thing to do.
A Legoland in Universal Orlando would draw five million guests a year; I don't think that a Legoland's yet been designed that could handle that.
The site selected in K.C. seems to be a ritzy exurb -- the sort of place with wealthy parents who'd shell out the bucks for Legoland visits. And the sort of place that wealthy exurbanites from other areas would find comfortable. But there would not be an existing base of tourists in the area that would overwhelm Legoland's capacity.
Avg. daily high temperatures for Kansas City, MO (1971-2000):Jan 35.7 Feb 42.4 Mar 53.9 Apr 64.6 May 74.3 Jun 83.3 Jul 88.7 Aug 86.8 Sep 78.6 Oct 67.0 Nov 51.6 Dec 39.4
Avg. daily low temperatures:Jan 17.9 Feb 23.5 Mar 33.3 Apr 43.5 May 54.0 Jun 63.1 Jul 68.4 Aug 66.3 Sep 57.1 Oct 45.8 Nov 33.3 Dec 22.3
To me, that says you could operate the park from late April to Halloween. Which would be a pretty typical seasonal operational calendar. Given the curtailed calendar and the location, I'd guess the park would really have to hustle to do one million visitors a year. About 750K would be more likely.